Epson 20 - Manual (Page 169)

Alternate Serial Port Check
Use this option to test the functions of an additional serial
communications (RS-232C) port. To perform the test you must insert
a special loop-back connector into the alternate serial port so that the
computer can check individual pins of the port.
This test is identical to the check for the primary serial port. For more
details, see the description of the Serial Port (RS-232C) Check.
Dot-matrix Printer Check
Use this option to check the following:
l
The operation of your printer in IBM-compatibility mode
l
The compatibility of your printer with the extended character set
your computer uses
The ability of your printer to produce bit-image graphics and
print images of the graphics screen.
When you select option 14 from the DEVICE LIST, you see this
prompt:
Is dot-matrix printer on-line (Y/N)?
Check that your printer is connected to the computer and that it is
turned on, loaded with paper, and online. Press Y and then Enter to
continue, or press N and Enter to return to the menu.
When you continue the test, the computer checks that the printer is
responding correctly. This test detects whether the printer is offline or
whether an interface error exists. If no errors occur, the computer
sends a repeating sequence of ASCII characters and bit-image data to
the printer until you press any key. The pattern looks like this:
Performing System Diagnostics C-25